>how many character that a variable can contain ??

Robert,
Would you be more specific on your need. I think only few ppl might know the actual limit. Practically no limit. While saying practically I mean in any language you wouldn't want system to allocate too much memory for a variable and instead would possibly use a file stream. Or you wouldn't want to have a string variable that's Mbs in size and operate on it using string functions.
Exceptions are possible as always.
I'd stay in documentation limits in any case :
Literal string : 255
String variable : 16Mb
Cetin